Hot-melt adhesive compositions comprising a partially (fumarized and/or maleinized) disproportionated rosin ester tackifier

ABSTRACT

A hot-melt adhesive composition containing an ethylene copolymer, wax and a tackifying resin as major components, the composition being characterized in that the tackifying resin is partially fumarinized and/or partially maleinized, disproportionated rosin ester.

Field of the Invention

This invention relates to hot-melt adhesive compositions, and moreparticularly to novel hot-melt adhesive compositions containing aspecific type of stabilized rosin ester as a tackifying resin andoutstanding in heat resistance and setting property.

BACKGROUND ART

Hot-melt adhesives are solid at an ordinary temperature. In use, theyare thermally melted, applied to substrates and set by being cooled tocause adhesion, whereby they exhibit bond strength.

These hot-melt adhesives have numerous advantages of having 100% solidscontent and being substantially free of fire hazards, capable of settingin a shorter period of time and easy to handle. Because of theseadvantages and with rapid spread of applicators, the hot-melt adhesiveshave found prevalent use in various fields such as bookbinding,packaging, woodbonding and the like.

Generally these hot-melt adhesives comprise: a base polymer such asethylene-vinyl acetate copolymer (EVA), ethylene-acrylate copolymer andlike ethylene copolymers, polyethylene, thermoplastic rubber, polyamide,polyurethane, polyester and like thermoplastic high-molecular-weightpolymers, etc.; a tackifying resin; and a viscosity-controlling agentsuch as various kinds of waxes. Widely used as the base polymer areethylene copolymers such as EVA, ethylene-acrylate and the like becausethey give adhesives favorable in respect of flexibility,thermostability, costs, etc. Useful tackifying resins include naturalresins such as rosin resin and terpene resin and petroleum resins.

Among these tackifying resins, common rosin resins have beenpredominantly used because they give adhesives high in adhesive propertyand cold resistance. But they can not provide adhesives satisfactory inthermostability and setting time. The rosin resin has beendisproportionated or hydrogenated or mixed with an expensive antioxidantto overcome the defect of low thermostability among the defects of rosinresin. However, the disproportionation or hydrogenation results in theproduction of adhesives as poor in setting property as those preparedfrom common rosin resins, although having an improved thermostability.Further a hydrogenated resin involves economical disadvantage, henceunfit for practical use. The use of antioxidant encounters otherdrawbacks of manufacturing adhesives unacceptable in coloration andodor, hence undesirable.

Terpene resins, chiefly terpene-phenol resins, give adhesives excellentin thermostability and setting time, but unsatisfactory in heatresistance, cold resistance and odor.

Use has been proposed and made of petroleum resins prepared bypolymerization of inexpensive petroleum fractions as tackifing resins inplace of rosin resins and terpene resins. While relatively good insetting property, the adhesives prepared from petroleum resins areinferior to those from the natural resins in compatibility,thermostability, adhesive property, cold resistance, etc.

As stated above, even if incorporating any of conventional tackifyingresins, hot-melt adhesives are poor in at least one of thermostability,compatibility, adhesive property, setting time and cold resistance.Hot-melt adhesives satisfactory in all of these characteristics have notbeen developed yet.

Directing attention to stabilized rosin esters relatively superior inthese characteristics to other conventional tackifying resins, weconducted extensive research to develop novel and useful hot-meltadhesives free of the foregoing drawbacks. As a result, we unexpectedlyfound that a specific type of stabilized rosin ester used as thetackifying resin gives hot-melt adhesives free of all the foregoingdrawbacks and particularly the poor setting property in which knownstabilized rosin esters have the most serious drawback. Based on thisnovel finding, we have accomplished this invention.

DISCLOSURE OF THE INVENTION

This invention provides hot-melt adhesive compositions containing anethylene copolymer, wax and a tackifying resin as major components, thecompositions being characterized in that the tackifying resin ispartially fumarinized and/or partially maleinized, disproportionatedrosin ester (hereinafter simply referred to as "stabilized rosinester").

The compositions of the present invention have all of the fundamentalproperties required of hot-melt adhesive compositions, namely: (1) beingthermally stable and free of coloration and skinning, (2) involving nophase separation due to good compatibility of the resin with the basepolymer and the wax, (3) neither giving off odor during application ofadhesives nor adversely affecting the work environment, (4) having goodadhesion to various substrates, and (5) possessing sufficientflexibility at low temperatures (hereinafter referred to as coldresistance). In addition, the present compositions have markedlyimproved properties, namely: (6) being outstanding in adhesive propertyat high temperatures (hereinafter referred to as heat resistance) and(7) being excellent in setting time for adhesion. With these properties,the compositions of the present invention are well suited and veryuseful in the present situation wherein it is desired to developadhesives excellent in heat resistance and setting time which are nowregarded as more important properties among the above characteristics inview of the recent development of packaging, assembly and the like.Especially the stabilized rosin ester contained as the tackifying resinin the present composition gives adhesives superior to those preparedfrom conventional rosin resins in thermostability, setting property,etc. and to those from terpene-phenol resin in heat resistance, coldresistance, odor, etc. Heretofore tackifying resins with theseproperties have not been developed.

It is critical in this invention that the stabilized rosin esterincluded as the tackifying resin in the present composition be partiallyfumarinized and/or partially maleinized, disproportionated rosin ester.Such resin can be prepared according to conventional processes, forexample, by reacting partially fumarinized rosin and/or partiallymaleinized rosin with alcohol to give a rosin ester which is thendisproportionated. The partially fumarinized rosin and partiallymaleinized rosin used in the process are not limited to particular kindsand can be prepared by conventional fumarinization or maleinizationmethods. For example, these partially fumarinized or maleinized rosinscan be prepared by mixing a rosin as the starting material with fumaricacid or maleic anhydride and heating the mixture for fumarinization ormaleinization to give an addition product of the Diels Alder type. Therosin used as the starting material can be any of gum rosin, wood rosinand tall oil rosin. The ratio of fumaric acid or maleic anhydride to beused relative to the rosin in the reaction is limited in view of thecompatibility of stabililized rosin ester (obtained by subsequentreaction) with the ethylene copolymer, the adhesive property of theadhesive, etc. Generally 1.3 to 20 mole %, preferably 2.6 to 13 mole %,of the fumaric acid or maleic anhydride is used based on the rosin. Ifless than 1.3 mole % thereof is present, hot-melt adhesives are producedwhich are poor in heat resistance and setting time, hence undesirable.The presence of more than 20 mole % thereof results in the production ofadhesives having reduced compatibility, consequently markedly impairedadhesive property, hence undesirable.

Trihydric or more polyhydric alcohol is preferably used as the otherstarting material, i.e. alcohol, to be esterified with the partiallyfumarinized rosin and/or partially maleinized rosin in view of themolecular weight and the softening point of the stabilized rosin esterto be produced by subsequent disproportionation reaction. Examples ofuseful polyhydric alcohols are glycerin, diglycerin, pentaerythritol,dipentaerythritol, etc. Preferred examples are glycerin andpentaerythritol.

The foregoing esterification reaction can be conducted in the samemanner as usual esterification. For example, the esterification can becarried out by heating the two components in the presence or absence ofa catalyst and with or without a solvent. Suitable solvents includearomatic solvents such as benzene, toluene and xylene. Examples ofuseful catalysts are acid catalysts such as sulfuric acid, acetic acidand p-toluenesulfonic acid; hydroxides of alkaline earth metals such ascalcium hydroxide; metal oxides such as magnesium oxide and calciumoxide; calcium carbonate; magnesium acetate and calcium acetate and likecatalysts commonly used for esterification. The amounts of the twocomponents are not particularly limited but can be suitably determinedaccording to the kind and acid value of the partially fumarinized rosinand/or partially maleinized rosin, softening point of the esterificationproduct thus obtained, etc. Generally the amounts thereof are such thatthe alcohol accounts for 10 to 15 % by weight of the total mixture.

The esterification product obtained above can be disproportionated byvarious processes heretofore known. More specifically, theesterification product is heated to about 220° to about 300° C. in thepresence of a catalyst commonly used for disproportionation.

Useful catalysts for disproportionation include noble metals such aspalladium, nickel and platinum; iodine and iodides such as iron iodide;sulfur compounds such as sulfur dioxide and iron sulfide; etc. In thisway, the stabilized rosin ester useful in the present invention isprepared. It is critical in this invention to use the stabilized rosinester with which the contemplated results of the present invention canbe achieved. The stabilization of esterification product, which can beachieved by the disproportionation described above, may be also feasibleby hydrogenation. However, when used as the tackifying resin, the resinobtained by hydrogenation provides adhesives poor in heat resistance andsetting time, and consequently can not be used to accomplish thecontemplated results of the present invention. Moreover, thehydrogenation is disadvantageous in respect of economy, ease ofreaction, etc., as compared with the disproportionation.

The stabilized rosin ester to be used in the present invention can beprepared by other processes as well as by the foregoing process. Forexample, a fumarinized or maleinized rosin serving as the startingmaterial is disproportionated, followed by esterification. Thedisproportionation and esterification in this process can be conductedat the same time. The reaction in these processes can be performed underthe same conditions as in the conventional processes, for instance,those to be employed in the known process stated above.

The stabilized rosin ester thus obtained generally has a softening pointof 110° to 140° C., preferably 115° to 135° C., a molecular weight ofabout 1000 to about 1800, preferably about 1100 to about 1500, and anacid value of approximately up to 20 and thus can be suitably used asthe tackifying resin of the present invention. The rosin esters having asoftening point far below 110° C. or a molecular weight exceedinglylower than 1000 are likely to give adhesives poor in heat resistance andinvolving delayed setting time. The resins with a softening point muchhigher than 140° C. or a molecular weight in large excess of 1800 areliable to produce adhesives lower in compatibility, heat resistance,cold resistance, etc. If the resin has an acid value of over 20, noproblem is caused, but the resin having too high an acid value tends toprovide adhesives with a slightly lower compatibility.

The pressure-sensitive adhesive compositions of the present inventioncontain the foregoing stabilized rosin ester as the tackifying resin, anethylene copolymer and wax as main components and can be prepared byheating with stirring these components. The ethylene copolymers usefulin this invention are those which are prepared by copolymerizingethylene with one or more of vinyl monocarboxylates and acrylates andwhich contain a polar component in an amount of about 10 to about 60% byweight, preferably 15 to 45% by weight, and have a melt index (MI) of0.1 to 1000, preferably 1 to 500. The term melt index used herein is thenumber of grams of the resin at 190° C. which can be forced in 10minutes by a 2160-g force according to ASTMD-1238. Examples of usefulwaxes are petroleum waxes such as paraffin wax and microcrystalline wax,natural wax, polyethylene wax, polypropylene wax, atactic polypropylenewax, etc. These waxes can be suitably selected according to a particularuse of hot-melt adhesives.

The proportions of the ethylene copolymer, wax and stabilized rosinester present in the hot-melt adhesive composition of this invention arenot particularly limited, but can be suitably selected from a wide rangedepending on the purpose of use and utility of the hot-melt adhesiveobtained, etc. For example, when used as the adhesives for papers, filmsof various plastics, aluminum foil and other materials associated withpackaging, the present adhesive composition containing a relativelysmall amount of ethylene copolymer is formulated and applied by coatingmethods such as roll coating, gravure coating, dip coating, etc.Generally the present compositions used for these purposes contain 10 to400 parts by weight of the wax and 20 to 300 parts by weight of thestabilized rosin ester per 100 parts by weight of the ethylenecopolymer. In use for work requiring a high degree of adhesion as inwoodbonding and bookbinding, use is made of the present compositionpredominantly containing the ethylene copolymer and stabilized rosinester so that the composition exhibits outstanding stiffness,flexibility and adhesive property. In this case, the present compositioncontains 20 to 200 parts by weight, preferably 100 to 130 parts byweight, of the stabilized rosin ester and 10 to 100 parts by weight,preferably 20 to 50 parts by weight, of the wax, per 100 parts by weightof the ethylene copolymer.

The present invention will be described below in greater detail withreference to reference examples and working examples to which theinvention, however, is limited in no way.

REFERENCE EXAMPLE 1

One hundred parts by weight of gum rosin was placed in a 4-necked flaskequipped with a stirrer, a condenser, a water separator and an inlettube for introducing nitrogen, and the mixture was heated with stirringin an atmosphere of nitrogen to 160° C. to give a molten mass.

One part by weight (2.6 mole % relative to the rosin) of fumaric acidwas added to the system, and the resulting mixture was heated withstirring to 220° C. to undergo fumarinization reaction. Thereafter 0.07part by weight of palladium carbon (5% of palladium supported on carbonand containing 50 % of water) was added and the mixture was maintainedat 280° C. for about 3 hours to complete the disproportionationreaction.

The resulting reaction product was filtered in molten state to removethe palladium carbon, giving partially fumarinized, disproportionatedrosin. The fumarinization product (100 parts by weight) andpentaerythritol (11.4 parts by weight) were charged into the reactor andthe mixture was subjected to esterification in an atmosphere of nitrogenat 285° C. for 12 hours, affording the stabilized rosin ester of thepresent invention.

The rosin ester thus obtained was found to have a softening point of114° C., acid value of 15.6 and Gardner color of 7.

REFERENCE EXAMPLES 2-7

The general procedure of Reference Example 1 was repeated except that atleast one of the kind of the rosin as the starting material, kind ofdibasic acid (fumaric acid or maleic anhydride), their amounts, kind ofpolyhydric alcohol and its amount was changed as shown below in Table 1which also demonstrates the stabilized rosin esters thus obtained.

                                      TABLE 1                                     __________________________________________________________________________               Dibasic acid                                                                            Polyhydric alcohol                                                       Amount    Amount                                                              (mole %   (weight %                                                           relative  relative                                                                            Softening                                                                           Acid                                                                              Gardner                             Ref. Ex.                                                                           Rosin Kind to rosin)                                                                          Kind to rosin)                                                                           point (°C.)                                                                  value                                                                             color                               __________________________________________________________________________    1    Gum rosin                                                                           Fumaric                                                                            2.6  Penta-                                                                             11.5  114   15.6                                                                              7                                              acid      erythritol                                               2    Gum rosin                                                                           Fumaric                                                                            7.8  Penta-                                                                             12.2  125   16.8                                                                              .sup. 6.sup.+                                  acid      erythritol                                               3    Gum rosin                                                                           Fumaric                                                                            13.0 Penta-                                                                             12.9  134   18.5                                                                              7                                              acid      erythritol                                               4    Gum rosin                                                                           Fumaric                                                                            7.8  Glycerin                                                                           12.9  112   10.5                                                                              6                                              acid                                                               5    Gum rosin                                                                           Fumaric                                                                            17.5 Glycerin                                                                           15.0  132    9.5                                                                              7                                              acid                                                               6    Gum rosin                                                                           Maleic                                                                             7.8  Penta-                                                                             12.2  126   17.5                                                                              7                                              anhydride erythritol                                               7    Tall oil                                                                            Fumaric                                                                            10.0 Penta-                                                                             12.6  122   16.7                                                                              9                                        resin acid      erythritol                                               __________________________________________________________________________

EXAMPLE 1

Using the stabilized rosin ester prepared in Reference Example 1, thecomposition of the present invention (compound) comprising the followingcomponents was prepared, and the test piece as stated below was producedby use of the compound.

Components for compound and preparation of test piece

    ______________________________________                                                             Amount (wt. part)                                        ______________________________________                                        EVA #150 (product of Mitsui Polychemical                                                             20                                                     Kabushiki Kaisha, Japan, vinyl acetate                                        content 33%, MI 25)                                                           EVA #220 (product of the same company as                                                             20                                                     above, vinyl acetate content 28%, MI 250)                                     Tackifying resin       50                                                     Low-molecular-weight polyethylene wax                                                                10                                                     (m.p. 240° F.)                                                         ______________________________________                                    

The components were placed in a beaker and thoroughly mixed at 180° C.to give the composition of the present invention. The composition wasapplied to a piece of aluminum foil to a thickness of 30 μ to produce atest piece.

EXAMPLES 2-7

Using various kinds of stabilized rosin esters prepared in ReferenceExamples 2 to 7, compounds were prepared in the same manner as inExample 1. Test pieces were produced by the same method as that ofExample 1 to evaluate the properties of the hot-melt adhesives.

COMPARATIVE EXAMPLES 1-6

Comparative compounds were prepared in the same manner as in Example 1except that the tackifying resins as shown below were employed in placeof the stabilized rosin ester prepared in Reference Example 1. Testpieces were made by the same method as that of Example 1.

    __________________________________________________________________________    Comp. Ex. No.                                                                         Tackifying Resin                                                                         Manufacturer                                                                           Trademark                                                                              Softening Point (°C.)             __________________________________________________________________________    1       C.sub.5 aliphatic petroleum                                                              Nippon Zeon                                                                            Quintone 100                                              resin               A-100                                             2       Pentaerythritol ester                                                                    Arakawa Kagaku                                                                         Pensel A 100                                              of rosin   Kogyo Kabushiki                                                               Kaisha                                                     3       Pentaerythritol ester                                                                    Arakawa Kagaku                                                                         Pensel C 125                                              of polymerized rosin                                                                     Kogyo Kabushiki                                                               Kaisha                                                     4       Pentaerythritol ester                                                                    Arakawa Kagaku                                                                         Malkyd No. 1                                                                           125                                              of maleinized rosin                                                                      Kogyo Kabushiki                                                               Kaisha                                                     5       Terpene-phenol resin                                                                     Yasuhara Yushi                                                                         YS Polyster T-130                                                                      130                                      6       Pentaerythritol ester                                                                    --       --       110                                              of disproportionated                                                          rosin                                                                 __________________________________________________________________________

COMPARATIVE EXAMPLE 7

The general procedure of Reference Example 1 was repeated using 100parts by weight of gum rosin and 3 parts by weight of fumaric acid,thereby giving fumarinized rosin. Into an autoclave were placed 107.8parts by weight of the fumarinized rosin and 0.5 part by weight ofdiatomaceous earth-nickel (50% of nickel supported on diatomaceousearth) and the mixture was maintained under 200 atmospheres and at 250°C. for 3 hours to complete the hydrogenation reaction. The resultingreaction product was filtered in molten state to remove the diatomaceousearth-nickel, giving partially fumarinized, hydrogenated rosin ester.

Esterification reaction was carried out in the same manner as inReference Example 1 by using 100 parts by weight of the fumarinizationproduct and 12.2 parts by weight of pentaerythritol, affording partiallyfumarinized, hydrogenated rosin ester. The rosin ester was found to havea softening point of 116° C., acid value of 17.0 and Gardner color of 8.

A compound was prepared in the same manner as in Example 1 by using theresin obtained above and a test piece was produced using the compound bythe same method as in Example 1.

Methods of tests for properties

The compounds and the test pieces prepared in the Examples andComparative Examples described above were tested for properties ofhot-melt adhesives by the following methods.

1. Thermostability

Fifty grams of the compound sample was placed in a 100 cc stainlessbeaker and was left to stand in an air-circulating oven at 200° C. for24 hours to observe the degree of coloration and the extent of skinningwith unaided eye.

2. Odor

The degree of odor was evaluated by smelling the odor emanating from thecompound being mixed at 180° C.

3. Compatibility

The compatibility was evaluated by observing with unaided eye theturbidity of the mixture in preparation of the compound at 180° C.

4. Heat resistance

Another piece of aluminum foil was put on the adhesive surface of thetest piece obtained by the foregoing method and heat-sealed at 180° C.under a pressure of 1 kg/cm² over 1 second.

The test piece (1 in. wide) obtained above was checked for heatresistance by finding out the was checked for heat resistance by findingout the temperature at which the foil piece was peeled off under a loadof 200 g at a temperature raised by 5° C./min according to the T-peelmethod.

5. Setting time

Test pieces were each heat-sealed to substrates respectively ofaluminum, wood and corrugated board at 180° C. under a pressure of 1kg/cm² over 1 second.

The test piece was peeled off by hand at specific intervals to measurethe time taken until no peeling occurred.

6. Cold resistance

The compound was shaped into a sheet 2 mm in thickness and the sheet wasleft to stand at 5° C. for 3 hours. It was checked whether cracks werecaused by folding the sheet under the foregoing conditions.

7. Adhesive property

A piece of aluminum or wood was put on the adhesive surface of each testpiece cut to a width of 1 in. and was heat-sealed at 180° C. under apressure of 1 kg/cm² over 1 second. The piece was peeled at an angle of180 degrees and at a velocity of 300 mm /min by a tensile tester.

Table 2 below shows the result thus obtained.

                                      TABLE 2                                     __________________________________________________________________________                      Setting time (sec)                                                                        Heat  Cold                                                                              Adhesive                              Thermo-      Compati-     Cor.                                                                              resist-                                                                             resist-                                                                           property (g/25 mm)                    stability                                                                              Odor                                                                              bility                                                                             Alum.                                                                             Wood                                                                              board                                                                             ance (°C.)                                                                   ance                                                                              Alum./alum.                                                                          Alum./wood                     __________________________________________________________________________    Ex.                                                                           No.                                                                           1   ⊚                                                                   ○                                                                          ⊚                                                                   18  19  19  74    ○                                                                          2500   2800                           2   ⊚                                                                   ○                                                                          ⊚                                                                   16  19  18  78    ○                                                                          2700   3000                           3   ⊚                                                                   ○                                                                          ○                                                                           10  13  12  76    ○                                                                          2300   2700                           4   ⊚                                                                   ○                                                                          ⊚                                                                   13  16  15  74    ○                                                                          2500   2700                           5   ⊚                                                                   ○                                                                          ○                                                                           11  15  13  76    ○                                                                          2400   2700                           6   ⊚                                                                   ○                                                                          ⊚                                                                   12  16  15  78    ○                                                                          2800   3000                           7   ⊚                                                                    ○ ˜Δ                                                          ⊚                                                                   13  15  14  78    ○                                                                          2700   2900                           Comp.                                                                         Ex.                                                                           No.                                                                           1   X    ○                                                                          X    20  21  21  60    X    500    700                           2   Δ                                                                            Δ                                                                           ⊚                                                                   23  26  25  61    ○                                                                          2500   2500                           3   Δ                                                                            Δ                                                                           ○                                                                           21  25  24  72    ○                                                                          2700   3000                           4   X    Δ                                                                           ⊚                                                                   28  30  30  74    ○                                                                          2500   3000                           5    ○ ˜Δ                                                           X   ⊚                                                                   19  22  20  61    X   2700   3100                           6   ⊚                                                                   ○                                                                          ⊚                                                                   25  25  26  61    ○                                                                          2400   2700                           7   ⊚                                                                   ○                                                                          ⊚                                                                   25  27  28  65    ○                                                                          2400   2700                           __________________________________________________________________________     Note:                                                                         ⊚ Excellent                                                     ○  Good                                                               Δ Fair                                                                  X No good                                                                

We claim:
 1. A hot melt adhesive composition containing an ethylenecopolymer, wax and a tackifying resin as major components, thecomposition being characterized in that the tackifying resin ispartially fumarinized and/or partially maleinized, disproportionatedrosin ester.
 2. A composition as defined in claim 1 wherein thetackifying resin is fumarinized or maleinized at a ratio of 1.3 to 20mole % based on the rosin.
 3. A composition as defined in claim 2wherein the tackifying resin is fumarinized or maleinized at a ratio of2.6 to 13 mole % based on the rosin.
 4. A composition as defined inclaim 1 wherein the tackifying resin is an ester of polyhydric alcohol.5. A composition as defined in claim 4 wherein the polyhydric alcohol isglycerin or pentaerythritol.
 6. A composition as defined in claim 1wherein the tackifying resin has a softening point of 110° to 140° C. 7.A composition as defined in claim 6 wherein the tackifying resin has asoftening point of 115° to 135° C.
 8. A composition as defined in claim1 wherein the tackifying resin has a molecular weight of 1000 to 1800.9. A composition as defined in claim 8 wherein the tackifying resin hasa molecular weight of 1100 to
 1500. 10. A composition as defined inclaim 1 wherein the ethylene copolymer is a copolymer of ethylene and atleast one of vinyl monocarboxylate and acrylate, the copolymercontaining 10 to 60% by weight of a polar component.
 11. A compositionas defined in claim 10 wherein 15 to 45% by weight of the polarcomponent is contained.
 12. A composition as defined in claim 1 whereinthe ethylene copolymer, wax and tackifying resin are used in a ratioranging from 100:10:20 to 100:400:300.
 13. A composition as defined inclaim 1 wherein the ethylene copolymer, wax and tackifying resin areused in a ratio ranging from 100:10:20 to 100:100:200.
 14. A compositionas defined in claim 1 wherein the ethylene copolymer, wax and tackifyingresin are used in a ratio ranging from 100:20:100 to 100:50:130.